Mixing and Nozzle Geometry Effects on Flame Structure and Stability

El-Mahallawy, F.M.; Abdelhafez, Ahmed; Mansour, Mohy S.

doi:10.1080/00102200600809324

Cited by 40 publications

(37 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In high Reynolds number turbulent flames, the quenching process is more complex. In an experimental study of partially premixed flames [9], it was shown that premixing of air to the fuel stream can decrease the flame stability regime, which is consistent with the laminar flame results of [7,8], however, a moderate partial premixing of air to the fuel stream can also improve the combustion stability. The fundamental physics behind this requires further investigation.…”

Section: Introductionsupporting

confidence: 54%

“…A quartz-glass conical nozzle, with a half cone angle of 26°, is mounted at the exit of the mixing chamber. Detailed information about the burner can be found in [9].…”

Section: Methodsmentioning

confidence: 99%

“…To generate turbulent partially premixed flames at high turbulent intensities, the concentric flow conical flame burner described in [9][10][11] is adopted. Previous studies, at a particular partial premixing condition, have shown that the flame is stabilized in the cone due to the presence of a triple flame at the leading flame front in the recirculation region induced by the entrainment of ambient air to the cone [12,13].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of Partial Premixing on Stabilization and Local Extinction of Turbulent Methane/Air Flames

Baudoin

Bai

Yan

et al. 2012

Flow Turbulence Combust

View full text Add to dashboard Cite

The stabilization characteristics and local extinction structures of partially premixed methane/air flames were studied using simultaneous OH-PLIF/PIV techniques, and large eddy simulations employing a two-scalar flamelet model. Partial premixing was made in a mixing chamber comprised of two concentric tubes, where the degree of partial premixing of fuel and air was controlled by varying the mixing length of the chamber. At the exit of the mixing chamber a cone was mounted to stabilize the flames at high turbulence intensities. The stability regime of flames was determined for different degree of partial premixing and Reynolds numbers. It was found that in general partially premixed flames at low Reynolds numbers become more stable when the level of partial premixing of air to the fuel stream decreases. At high Reynolds numbers, for the presently studied burner configuration there is an optimal partial premixing level of air to the fuel stream at which the flame is most stable. OH-PLIF images revealed that for the stable flames not very close to the blowout regime, significant local extinction holes appear already. By increasing premixing air to fuel stream successively, local extinction holes grow in size leading to eventual flame blowout. Local flame extinction was found to frequently attain to locations where locally high velocity flows impinging to the flame. The local flame extinction poses a future challenge for model simulations and the present flames provide a possible test case for such study. IntroductionPartially premixed flames, defined as flames where the compositions of the mixture vary from fuel-rich to stoichiometry and fuel-lean [1], are found in many engineering applications. In modern internal combustion engines using multiple injections of fuel to control emissions, partially premixed charge are typically formed before ignition. Due to the presence of rich, lean and stoichiometric mixtures in partially premixed flames, lean and rich premixed flame fronts exist in the leading front followed by the main diffusion flame [2][3][4]. The combustion characteristics of partially premixed flames are not well understood and modeling of partially premixed flames is challenging [1,2,5].Local flame quenching and re-ignition in laminar and turbulent flames is an issue that has attracted the attention of recent research. Once a non-premixed flame is locally quenched, edge flame exists at the extremity of the reaction zones, where the flame progressively evolves to partially premixed flames [6]. The critical strain rate for quenching of partially premixed flames is influenced by the degree of partial premixing. For laminar flames, experimental and theoretical studies [7,8] using a counter flow configuration showed that partial premixing of fuel to the air stream can increase the quenching strain rate, whereas partial premixing of air to the fuel stream can decrease the critical quenching strain rate. In high Reynolds number turbulent flames, the quenching process is more complex. In an

show abstract

Section: Introductionsupporting

confidence: 54%

“…A quartz-glass conical nozzle, with a half cone angle of 26°, is mounted at the exit of the mixing chamber. Detailed information about the burner can be found in [9].…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Partial Premixing on Stabilization and Local Extinction of Turbulent Methane/Air Flames

Baudoin

Bai

Yan

et al. 2012

Flow Turbulence Combust

View full text Add to dashboard Cite

show abstract

“…Thus the conical nozzle provides a good stabilization environment. In addition, an optimum level of partial premixing for the highest stability can be achieved in this burner [16]. The temperature and gas species concentrations inside and downstream the nozzle are investigated by Elbaz [19] for Liquid Petroleum Gas (LPG) partial premixed flames.…”

Section: Introductionmentioning

confidence: 99%

“…The higher stability characteristic of the CFCN burner, as compared to a nozzle jet burner, is due to the conical shape of the nozzle and control of the level of partial premixing. The effects of the degree of partial premixing, the cone angle and the jet equivalence ratio on the flame stability and structure have previously been investigated [16]. Measurements and numerical study were conducted inside and downstream the conical nozzle in order to explore the stabilization mechanism and investigate the flame structure of partially premixed flames [17,18] under different equivalence ratios and degrees of partial premixed.…”

Section: Introductionmentioning

confidence: 99%

The flow field structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner with coflow

Elbaz

Zayed

Samy

et al. 2016

Experimental Thermal and Fluid Science

View full text Add to dashboard Cite

The flow field structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner with coflow KAUST Repository a b s t r a c tThe stability limits, the stabilization mechanism, and the flow field structure of highly stabilized partially premixed methane flames in a concentric flow conical nozzle burner with air co-flow have been investigated and presented in this work. The stability map of partial premixed flames illustrates that the flames are stable between two extinction limits. A low extinction limit when partial premixed flames approach non-premixed flame conditions, and a high extinction limit, with the partial premixed flames approach fully premixed flame conditions. These two limits showed that the most stable flame conditions are achieved at a certain degree of partial premixed. The stability is improved by adding air co-flow. As the air co-flow velocity increases the most stable flames are those that approach fully premixed. The turbulent flow field of three flames at 0, 5, 10 m/s co-flow velocity are investigated using Stereo Particle Image Velocimetry (SPIV) in order to explore the improvement of the flame stability due to the use of air co-flow. The three flames are all at a jet equivalence ratio (U j ) of 2, fixed level of partial premixing and jet Reynolds number (Re j ) of 10,000. The use of co-flow results in the formation of two vortices at the cone exit. These vortices act like stabilization anchors for the flames to the nozzle tip. With these vortices in the flow field, the reaction zone shifts toward the reduced turbulence intensity at the nozzle rim of the cone. Interesting information about the structure of the flow field with and without co-flow are identified and reported in this work.

show abstract

A Study of Structure and Entropy Generation in Confined Biogas Coflow Diffusion Flames

Kumar

Kumaran

Raghavan

2022

Recent Advances in Energy Technologies

View full text Add to dashboard Cite

Mixing and Nozzle Geometry Effects on Flame Structure and Stability

Cited by 40 publications

References 24 publications

Effect of Partial Premixing on Stabilization and Local Extinction of Turbulent Methane/Air Flames

Effect of Partial Premixing on Stabilization and Local Extinction of Turbulent Methane/Air Flames

The flow field structure of highly stabilized partially premixed flames in a concentric flow conical nozzle burner with coflow

A Study of Structure and Entropy Generation in Confined Biogas Coflow Diffusion Flames

Contact Info

Product

Resources

About